Competence Assessment for Standing Trial for Defendants with Mental Retardation (CAST*MR)

The Competence Assessment for Standing Trial for Defendants With Mental Retardation (CAST*MR) consists of 50 questions and was designed to assess defendants’ understanding of basic legal concepts, ability to assist their attorneys, and ability to relate important information regarding their own legal circumstances. Its purpose is to assist forensic evaluators in determining competency in defendants with mental retardation. The CAST*MR demonstrated test-retest reliability and validity in several studies prior to its publication.

Competence to stand trial is critical for ensuring due process rights for defendants in the criminal justice system. The doctrine of competence to stand trial has its origins in early English common law and relates to the accepted belief that a defendant cannot be tried in absentia. It is thought that trying an incompetent defendant who cannot understand and participate in the proceedings is equivalent to trying someone in absentia. Hence, competency is essential for due process and fundamental fairness.

The criteria for judging competence to stand trial was articulated in the 1960 Supreme Court decision Dusky v. United States. Dusky states that to be competent to stand trial, a defendant must have a “rational and factual understanding of the proceedings” and be able to consult with his or her attorney with a “reasonable degree of rational understanding” (p. 402).

Application of the doctrine of competence to stand trial to defendants with mental retardation requires special consideration because of the unique nature of the disability. According to the American Association on Intellectual and Developmental Disabilities (previously AAMR), “mental retardation is a disability characterized by significant limitations both in intellectual functioning and in adaptive behavior as expressed in conceptual, social, and practical adaptive skills. This disability originates before age 18” (p. 1). Because of the high risk that intellectual and adaptive behavior limitations may negatively affect the necessary elements of competence to stand trial, particular care must be taken to conduct an authentic assessment in order to preserve fairness.

Description of the CAST*MR

The CAST*MR was developed by Caroline Everington and Ruth Luckasson to assist forensic evaluators in determining competency in defendants with mental retardation. The first two sections of the CAST*MR consist of 40 multiple-choice questions. This format was chosen as it provides a quick and reliable means of assessing defendants’ understanding. Many persons with mental retardation have difficulty with expressive language and exhibit acquiescence in assessment situations. This format helps correct for those problems. As will be discussed later, CAST*MR results should be supplemented with additional information relevant to the defendant’s competency and necessary for clinical judgment.

The first section, Basic Legal Concepts, contains 25 multiple-choice items and addresses understanding of the roles of key players in the process—for example, judge, attorney, prosecutor, witness—and important procedures such as a plea bargain and trial. In the second section, Skills to Assist in Defense, the defendants are presented with 15 scenarios that involve the choices they must make about their case or when working with their attorneys. This section is also presented in a multiple-choice format. In the final section, Understanding Case Events, the defendants must answer a series of key questions about the circumstances of their arrest and the charges.

CAST*MR Validity and Reliability

An expert appraisal process was used to develop items for the instrument. The first versions were field tested with individuals with mental retardation as well as college students. Validation studies were conducted before publication.

There have been two primary validation studies conducted on the CAST*MR. Caroline Everington conducted the first study with defendants with and without mental retardation at the pretrial level. In the first study, it was determined that the instrument successfully discriminated between groups of defendants and had an acceptable classification rate. Test-retest reliability and internal consistency analyses yielded acceptable results as well.

A second validation study was conducted by Caroline Everington and Charles Dunn using defendants with mental retardation who were referred for evaluations of competence to stand trial. The second study replicated the results of the Everington study.

Caroline Everington, Katherine DeBerge, and Daria Mauer, studying adults with mental retardation, found that CAST*MR scores were significantly correlated with language subtests on the Woodcock-Johnson Tests of Cognitive Ability and these language tests were good predictors of CAST*MR performance. This finding supports the use of assessments of language ability in competence evaluations involving persons with mental retardation.

While there are no findings regarding malingering on the CAST*MR, Caroline Everington, Heidi Notario-Smull, and Mel Horton found that individuals in the higher-IQ range of mental retardation could alter their performance when asked to do poorly. These individuals scored lower than a group of defendants with mental retardation who had been evaluated as incompetent to stand trial and the control group of defendants with mental retardation who took the test under standard conditions. This reaffirms the need to supplement scores with additional information.

Appropriate Use of the CAST*MR

It is important that competency evaluations of persons with mental retardation include multiple sources of information. A single test score should not be the sole determinant of defendant competency. An evaluation test battery for persons with mental retardation should include an individually administered global test of intelligence and assessments of expressive and receptive language, academic skills, and adaptive behavior. Social history provides additional information on cognitive and academic skills and previous diagnoses. Interviews with key individuals who have known the defendant over time provides information relevant to competency, such as the defendant’s problem-solving and decision-making skills. These sources provide corroborative information that can assist in the interpretation of CAST*MR results.

Finally, CAST*MR results should be supported with additional information on the defendant’s psycholegal abilities. Other sources include information gained through questioning in the clinical interview and can include an additional assessment of competence to stand trial. It is important to check for understanding by having the defendant explain concepts in his or her own words. Decisional competency is a critical area for individuals with mental retardation. It is important to query the individual on his or her understanding of the defense strategy and his or her legal options.

The CAST*MR is published by IDS in Columbus, Ohio, and is used by evaluators throughout the United States.


  1. Dusky v. United States, 362 U.S. 402 (1960).
  2. Everington, C., DeBerge, K., & Mauer, D. (2001). The relationship between language skills and competence to stand trial abilities in persons with mental retardation. Journal of Psychiatry and Law, 28, 475—192.
  3. Everington, C., & Dunn, C. (1995). A second validation study of the competence assessment for standing trial for defendants with mental retardation. Criminal Justice and Behavior, 22, 44-59.
  4. Everington, C., & Luckasson, R. (1992). The competence assessment for standing trial for defendants with mental retardation (CAST*MR). Worthington, OH: IDS.
  5. Everington, C., Notario-Smull, H., & Horton, M. (in press). Can defendants with mental retardation successfully fake their performance on a test of competence to stand trial? Behavioral Sciences and the Law.

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